You are misrepresenting that position, whether intentionally or in error. Whereas a zygote is human life from conception, that doesn't entail that it is a person. That is, think about the morally relevant qualities that defines what a person is. A zygote doesn't have these qualities, it just has the potential of developing them. A zygote is merely a clump of cells, containing, at that moment, no more personhood than any other randomly selected clump of cells.
By contrast, animals do have these qualities. This is an argument (among many) that animal advocates make and why they can be perfectly comfortable with abortions as late as 24 weeks or so, when the capacities for personhood manifest themselves, but still demand that animals be afforded moral consideration.
Now, if you want to use the argument of ensoulment (and that it takes place at conception), that's fine and, naturally, abortion would be murder. But ensoulment is a religious concept and doesn't carry any currency in a system that claims a separation of Church and State; that is, just because one believes that a zygote has a soul doesn't entail that such an opinion be imposed upon the person who doesn't believe it. From a legal standpoint, the issue has to be one of rights, and a person has them, and a non-person doesn't.
Nemesio